Standards for WLAN (Wireless Local Area Network) technologies are developed as IEEE 802.11 standards. Among amendments of the IEEE 802.11 standards, IEEE 802.11a/b provide transmission rates of 11 Mbps (IEEE 802.11b) and 54 Mbps (IEEE 802.11a) using an unlicensed band at 2.4 GHz or 5 GHz. IEEE 802.11g provides a transmission rate of 54 Mbps using OFDM at 2.4 GHz. IEEE 802.11n provides a transmission rate of 300 Mbps for 4 spatial streams using MIMO-OFDM (Multiple Input Multiple Output—Orthogonal Frequency Division Multiplexing). IEEE 802.11n supports channel bandwidths of up to 40 MHz and, in this case, provides a transmission rate of 600 Mbps.
IEEE 802.11af standards regulate WLAN operation of an unlicensed device in a TV whitespace zone.
TV whitespace (referred to as ‘TVWS’ hereinafter) is a frequency allocated to broadcast TV and can include UHF and VHF bands. While the TVWS can include 54 MHz to 698 MHz (US and Korea), part of these frequency bands may not be used for unlicensed devices in some countries.
In a frequency band, an STA operating as an unlicensed device can use an available channel that is not used by a licensed device. Accordingly, it is important for an STA that needs to use TVWS to acquire information about an available channel that is not used by a licensed device. To achieve this, the STA can perform spectrum sensing at the location thereof in order to obtain information on the available channel.
Unlicensed devices using TVWS need to provide a protection function for operations of licensed devices (which may be referred to as ‘incumbent users’ or ‘primary users’). That is, when an incumbent user such as a microphone uses a specific band used by an STA, the STA needs to stop using a channel corresponding to the band in order to protect the incumbent user.
To this end, STAB may require a frequency sensing mechanism. An energy detection scheme, a signature detection scheme and the like can be used as the frequency sensing mechanism. An STA can determine that a band is being used by an incumbent user if the intensity of a received signal exceeds a predetermined value, or when a DTV preamble is detected.
To overcome the problem of coexistence between unlicensed devices, a signaling protocol such as a common beacon frame, a frequency mechanism, or the like may be required for the unlicensed devices.